At present, digital data carriers with optical recording, storage and reading experience fast spreading. Usually, the data is recorded by local alteration of optical thickness or the active media reflection ratio, while reading takes place by phase or amplitude changes of the laser beam in the recorded spots.
The most cheap and absolute optical carriers are CD ROM and WORM discs. However, the capacity and signal/noise ratio of the existing optical discs is not high enough for the developed computers and videosystems of the new generation. Thus, there are intensive development of advanced optical memory systems with increased record density, high signal/noise ratio, increased storage and usage stability and low cost. The promising ways of increasing optical carrier capacity are:                increased number of active bits per active layer due to reduced pit length and increased number of pits; and        multilayer disc creation.        
These ways were realized in the recently launched DVD standard, where pits are half in size, and the number of layers reaches 4—two from each side of the substrate. This allows reaching 25 GB capacity on disc.
At the same time, further increase of active layers on discs with reading by means of reflection causes a rapid rise in the system price and lowers the quality of recorded data reproduction. Thus, future increase of disc capacity is not possible. The patents JP 63,195,838 (12.08.1988) and JP 02,308,439 (21.12.1990) describe reading by means of fluorescence. The principle idea is that after recording the recorded spots are non-fluorescent, and the background is fluorescent. At reading, the relevant laser beam excites fluorescent light, which is registered on the detector.
The above patents describe single-layer optical discs with laser recording, i.e. of WORM type.
At the same time, the main advantage of fluorescent reading is its suitability for three-dimensional optical memory carriers, such as multilayer discs. [B. Glushko, V. Krugkin, E. Levich].
The principle construction of a multilayer optical disc with fluorescent reading is described in [B. Glushko, US Provisional Patent Application Aug. 5, 1997, N 25457].
Single-layer optical discs, where data is recorded in pits or spiral grooves filled with fluorescent material, are laminated on each other to form a multilayer system, where active layers containing fluorescent pits or grooves 0.5–1.0 μm in depth are separated by inactive intermediate layers of 20–50 μm in depth, that are transparent for the excitation laser wavelength and fluorescent light. Fluorescent media for a multilayer optical disc with fluorescent reading shall meet a range of requirements, the most important being:
1. Fluorescent media absorption range shall coincide with the reading laser wavelength.
2. Quantum yield of fluorescent media shall be the highest possible and shall stay the same during long-term storage and use.
3. Absorption and fluorescence ranges shall not overlap significantly so not to cause repeated absorption of fluorescent light.
4. Fluorescent composition shall not disperse the passing excitation radiation and fluorescent light.
5. Fluorescent light shall also coincide well with the matrix and shall not migrate from it.
6. Fluorescent composition shall fill the pits or grooves well and shall not tincture the space in between.
7. The solution used for filling pits or grooves shall not dissolve the substrate, carrying pits or grooves, or change their geometry and size.
8. Refraction ratio of the fluorescent composition shall be close to the one of the substrate, carrying pits or grooves.
9. Characteristics of the fluorescent composition shall not be effected by storage or use of a multilayer optical disc.
All these requirements make it a non-trivial task to solve. It is especially difficult to achieve high intensity of fluorescence from the active layer, if we consider it to be 100–500 nm thick, with the concentration of fluorescent dye equal to 3–20×10−2 Mol per kg of polymer. At such concentrations, the intensity of fluorescence from most of the organic luminophores will be rapidly reduced or can disappear due to the formation of associated forms of the dye with sandwich structure in the polymer. Such forms are non-fluorescent and they extinguish fluorescence of monomeric forms of the dye. Ability of the dye to form dimers and other associates is connected to the composition and structure of the polymeric matrix, used plasticizers and other ingredients of the polymeric composition. However, such high concentrations of the dye (3–20×10−2 Mol/kg) nearly always cause formation of associates.
Recently the medias for high-density optical CD ROM and WORM discs with fluorescent reading, including multilayer discs, were described in [M. Alperovich, E. Levich, I. Zuhl, et al. US Provisional Patent Appl. N Fluorescent Composition for production of the optical memory discs of CD ROM type; M. Alperovich, E. Levich, I. Zuhl, et al. US Provisional Patent Appln. Organic dye-in-polymer (DIP) medium for WORM disks with fluorescent reading; M. Alperovich, E. Levich, I. Zuhl, et al. US Provisional Patent Appln. Optical recording medium for fluorescent WORM discs; M. Alperovich, E. Levich, I. Zuhl, et al. US Provisional Patent Appln. Optical recording medium for fluorescent WORM disk including penetrated ion pairs in organic dyes].
The proposed fluorescent compositions were used for production of CD ROM and WORM discs with fluorescent reading, including multilayer structures. The recorded digital data was read on special drives, providing registration of the fluorescent signal. At the same time, further increase of fluorescence intensity from active layers of the optical discs is needed to increase stability and quality of the read data, to simplify the construction and to lower cost of production of the reading devices for fluorescent discs. This will also allow increasing the number of active layers on multilayer discs, thus increasing the optical memory capacity.